The DCCT is an international study supported by NIDKK whose purpose is to compare the effects of two treatment regimens designed to produce different levels of metabolic control on the clinical course of early vascular complications in persons with IDDM. The 2 treatment schedules are called Standard, a conventional insulin regimen; Experimental, an intensive insulin regimen. Blood glucose & HgA1c will be used as the primary indicators of metabolic control. Diabetic retinopathy will be the main outcome assessed.